DTC P0156[AJ (3.0L Duratec)]

DTC P0156	Rear HO2S (LH) sensor circuit malfunction
DETECTION CONDITION	• The PCM monitors input voltage form rear HO2S (LH) continuously. If the maximum or minimum input voltage exceeds calibrated range, the PCM determines rear HO2S (LH) sensor circuit is malfunction.
POSSIBLE CAUSE	• Pinched, shorted, and corroded wiring and pins • Crossed sensor wires • Exhaust leaks • Contaminated or damaged sensor

DTC P0156

Rear HO2S (LH) sensor circuit malfunction

DETECTION CONDITION

• The PCM monitors input voltage form rear HO2S (LH) continuously. If the maximum or minimum input voltage exceeds calibrated range, the PCM determines rear HO2S (LH) sensor circuit is malfunction.

POSSIBLE CAUSE

• Pinched, shorted, and corroded wiring and pins

• Crossed sensor wires

• Exhaust leaks

• Contaminated or damaged sensor

STEP	INSPECTION	ACTION
1	VERIFY FREEZE FRAME DATA HAS BEEN RECORDED • Has FREEZE FRAME DATA been recorded?	Yes	Go to the next step.
No	Record the FREEZE FRAME DATA on the repair order, then go to the next step.
2	VERIFY SERVICE INFORMATION AVAILABILITY • Verify related Service Information availability. • Is any related Service Information available?	Yes	Perform repair or diagnosis according to the available Service Information. • If the vehicle is not repaired, go to the next step.
No	Go to the next step.
3	IDENTIFY TRIGGER DTC FOR FREEZE FRAME DATA • Is DTC P0156 on the FREEZE FRAME DATA?	Yes	Go to the next step.
No	Go to the FREEZE FRAME DATA DTC inspection. (See DTC TABLE[AJ (3.0L Duratec)].)
4	VISUALLY INSPECT FOR REAR HO2S (LH) Note • Refer to the PCM connector pin number in the beginning of this pinpoint test. • If necessary to address all Continuous Memory Ignition and Misfire DTCs, if received during Continuous Memory testing, before addressing any KOER rear HO2S (LH) • Visually inspect for rear HO2S (RH) followings: ― Pinched, shorted and corroded wiring and pins ― Crossed sensor wires ― Exhaust leakage ― Oil or water contamination ― Contaminated or damaged sensor • Were any concerns found during inspection?	Yes	Repair or replace malfunctioning part, then go to Step 14.
No	Go to the next step.
5	CHECK FOR KOER DTCS P1137, P1157, P1138, P1158, P2270, P2271, P2272 AND P2273 • Connect the M-MDS to DLC-2. • Start the engine. • Engine at 2,000 rpm for 3 min. • Activate KOER self test. • Check for DTCs. • Is DTC P1137, P1138, P1157, P1158, P2270, P2271, P2272 or P2273 present?	Yes	Go to the next step.
No	Intermittent malfunction exist, go to Step 14.
6	CHECK EXHAUST SYSTEM FOR LEAKS Note • Any exhaust leaks between the engine and the end of the catalyst can cause DTC P0156. • Place vehicle on a host, transaxle in P position, parking brake applied, raise vehicle. • Inspect the following: ― Exhaust flanges for leaks ― Rear HO2S (LH) tightening torque ― Check for punctures and cracks in catalyst and pipes leading to them. • Is an exhaust leak present?	Yes	Repair or replace malfunctioning part, then go to Step 14.
No	Go to the next step.
7	CHECK REAR HO2S (LH) SIGNAL LEVEL TOO HIGH Note • Fuel calculations can be affected by abnormal air leaks. • Carefully inspect the following areas for potential air leaks: ― Hoses connecting to MAF/IAT sensor assembly. ― Hoses connecting to throttle body. ― Intake manifold gasket leaks. ― PCV disconnected. ― The vacuum lines are disconnected. ― Improperly seated engine oil dipstick, tube or oil fill cap. ― Exhaust gas leaks at flanges and gaskets. • Raise the vehicle on a hoist and make sure the vehicle is level. • Visually inspect for the following: ― Exhaust leaks at flanges and gaskets. ― Rear HO2S (LH) not torqued to specification. ― Physical exhaust system concerns. ― Aftermarket exhaust. ― Punctures or cracks in the catalyst. • Where any of the above conditions or concerns found during inspection?	Yes	Repair or replace malfunctioning part, then go to Step 14.
No	Go to the next step.
8	CHECK REAR HO2S (LH) HARNESS CIRCUIT FOR SHORT TO VPWR AND GROUND • Disconnect the PCM and rear HO2S (LH). • Measure the resistance between following terminals at the PCM harness side connector. ― Between terminal 61 and 24, 51, 71, 76, 90, 91, 97, 103 • Is the resistance greater than 10,000 ohms?	Yes	Go to the next step.
No	Repair for short circuit, then go to Step 14.
9	CHECK REAR HO2S (LH) SIGNAL CIRCUIT AND REAR HO2S (LH) SIGNAL RETURN CIRCUITS FOR OPEN IN HARNESS • Measure resistance between the following at the harness side connector. ― Between rear HO2S (LH) terminal A and PCM terminal 96 ― Between rear HO2S (LH) terminal C and PCM terminal 91 ― Between rear HO2S (LH) terminal B and PCM terminal 61 • Is the resistance less than 5.0 ohms?	Yes	Go to the next step.
No	Repair for open circuit, then go to Step 14.
10	CHECK REAR HO2S (LH) CIRCUIT VOLTAGE • Connect the PCM and rear HO2S (LH). • Connect the M-MDS to DLC-2. • Turn the ignition switch to the ON position. • Access the O2S22 PID. • Is the voltage greater than 1.5 V?	Yes	Go to Step 13.
No	Go to the next step.
11	CHECK REAR HO2S (LH) GROUND CIRCUIT IN PCM • Disconnect the PCM. • Measure the resistance between terminal 91 and 24, 51, 76, 103 at the PCM connector. • Is the resistance less than 5.0 ohms?	Yes	Go to the next step.
No	Replace the PCM, then go to Step 14.
12	REAR HO2S (LH) CIRCUIT CHECK • Connect the PCM. • Rear HO2S (LH) disconnected. • Jumper terminal C and B at the rear HO2S (LH) harness side connector. • Turn the ignition switch to the ON position. • Access the O2S22 PID. • Is the O2S22 PID value greater than 1.5 V?	Yes	Replace the rear HO2S (LH), then go to Step 14.
No	Replace the PCM, then go to Step 14.
13	CHECK FOR OVER VOLTAGE ON REAR HO2S (LH) CIRCUIT IN PCM • Turn the ignition switch to the ON position. • Rear HO2S (LH) disconnected. • Measure the voltage for following: ― Between terminal D at the rear HO2S (LH) harness side connector and battery negative post. ― Between terminal B at the rear HO2S (LH) harness side connector and battery negative post. • Is the voltage greater than 1.5 V?	Yes	Replace the PCM, then go to the next step.
No	Replace the rear HO2S (LH), then go to the next step.
14	VERIFY TROUBLESHOOTING OF DTC P0156 COMPLETED • Make sure to reconnect all disconnected connectors. • Clear the DTC from the PCM memory using the M-MDS. • Drive the vehicle at 64 km/h {40 MPH} for at 5 min. • Is the PENDING CODE same DTC present?	Yes	Replace the PCM, then go to the next step. (See PCM REMOVAL/INSTALLATION[AJ (3.0L Duratec)].)
No	Go to the next step.
15	VERIFY AFTER REPAIR PROCEDURE • Perform “AFTER REPAIR PROCEDURE”. (See AFTER REPAIR PROCEDURE[AJ (3.0L Duratec)].) • Is there any DTC present?	Yes	Go to the applicable DTC inspection. (See DTC TABLE[AJ (3.0L Duratec)].)
No	Troubleshooting completed.

STEP

INSPECTION

ACTION

VERIFY FREEZE FRAME DATA HAS BEEN RECORDED

• Has FREEZE FRAME DATA been recorded?

Yes

Go to the next step.

Record the FREEZE FRAME DATA on the repair order, then go to the next step.

VERIFY SERVICE INFORMATION AVAILABILITY

• Verify related Service Information availability.

• Is any related Service Information available?

Yes

Perform repair or diagnosis according to the available Service Information.

• If the vehicle is not repaired, go to the next step.

Go to the next step.

IDENTIFY TRIGGER DTC FOR FREEZE FRAME DATA

• Is DTC P0156 on the FREEZE FRAME DATA?

Yes

Go to the next step.

Go to the FREEZE FRAME DATA DTC inspection.

(See DTC TABLE[AJ (3.0L Duratec)].)

VISUALLY INSPECT FOR REAR HO2S (LH)

Note

• Refer to the PCM connector pin number in the beginning of this pinpoint test.

• If necessary to address all Continuous Memory Ignition and Misfire DTCs, if received during Continuous Memory testing, before addressing any KOER rear HO2S (LH)

• Visually inspect for rear HO2S (RH) followings:

― Pinched, shorted and corroded wiring and pins

― Crossed sensor wires

― Exhaust leakage

― Oil or water contamination

― Contaminated or damaged sensor

• Were any concerns found during inspection?

Yes

Repair or replace malfunctioning part, then go to Step 14.

Go to the next step.

CHECK FOR KOER DTCS P1137, P1157, P1138, P1158, P2270, P2271, P2272 AND P2273

• Connect the M-MDS to DLC-2.

• Start the engine.

• Engine at 2,000 rpm for 3 min.

• Activate KOER self test.

• Check for DTCs.

• Is DTC P1137, P1138, P1157, P1158, P2270, P2271, P2272 or P2273 present?

Yes

Go to the next step.

Intermittent malfunction exist, go to Step 14.

CHECK EXHAUST SYSTEM FOR LEAKS

Note

• Any exhaust leaks between the engine and the end of the catalyst can cause DTC P0156.

• Place vehicle on a host, transaxle in P position, parking brake applied, raise vehicle.

• Inspect the following:

― Exhaust flanges for leaks

― Rear HO2S (LH) tightening torque

― Check for punctures and cracks in catalyst and pipes leading to them.

• Is an exhaust leak present?

Yes

Repair or replace malfunctioning part, then go to Step 14.

Go to the next step.

CHECK REAR HO2S (LH) SIGNAL LEVEL TOO HIGH

Note

• Fuel calculations can be affected by abnormal air leaks.

• Carefully inspect the following areas for potential air leaks:

― Hoses connecting to MAF/IAT sensor assembly.

― Hoses connecting to throttle body.

― Intake manifold gasket leaks.

― PCV disconnected.

― The vacuum lines are disconnected.

― Improperly seated engine oil dipstick, tube or oil fill cap.

― Exhaust gas leaks at flanges and gaskets.

• Raise the vehicle on a hoist and make sure the vehicle is level.

• Visually inspect for the following:

― Exhaust leaks at flanges and gaskets.

― Rear HO2S (LH) not torqued to specification.

― Physical exhaust system concerns.

― Aftermarket exhaust.

― Punctures or cracks in the catalyst.

• Where any of the above conditions or concerns found during inspection?

Yes

Repair or replace malfunctioning part, then go to Step 14.

Go to the next step.

CHECK REAR HO2S (LH) HARNESS CIRCUIT FOR SHORT TO VPWR AND GROUND

• Disconnect the PCM and rear HO2S (LH).

• Measure the resistance between following terminals at the PCM harness side connector.

― Between terminal 61 and 24, 51, 71, 76, 90, 91, 97, 103

• Is the resistance greater than 10,000 ohms?

Yes

Go to the next step.

Repair for short circuit, then go to Step 14.

CHECK REAR HO2S (LH) SIGNAL CIRCUIT AND REAR HO2S (LH) SIGNAL RETURN CIRCUITS FOR OPEN IN HARNESS

• Measure resistance between the following at the harness side connector.

― Between rear HO2S (LH) terminal A and PCM terminal 96

― Between rear HO2S (LH) terminal C and PCM terminal 91

― Between rear HO2S (LH) terminal B and PCM terminal 61

• Is the resistance less than 5.0 ohms?

Yes

Go to the next step.

Repair for open circuit, then go to Step 14.

CHECK REAR HO2S (LH) CIRCUIT VOLTAGE

• Connect the PCM and rear HO2S (LH).

• Connect the M-MDS to DLC-2.

• Turn the ignition switch to the ON position.

• Access the O2S22 PID.

• Is the voltage greater than 1.5 V?

Yes

Go to Step 13.

Go to the next step.

CHECK REAR HO2S (LH) GROUND CIRCUIT IN PCM

• Disconnect the PCM.

• Measure the resistance between terminal 91 and 24, 51, 76, 103 at the PCM connector.

• Is the resistance less than 5.0 ohms?

Yes

Go to the next step.

Replace the PCM, then go to Step 14.

REAR HO2S (LH) CIRCUIT CHECK

• Connect the PCM.

• Rear HO2S (LH) disconnected.

• Jumper terminal C and B at the rear HO2S (LH) harness side connector.

• Turn the ignition switch to the ON position.

• Access the O2S22 PID.

• Is the O2S22 PID value greater than 1.5 V?

Yes

Replace the rear HO2S (LH), then go to Step 14.

Replace the PCM, then go to Step 14.

CHECK FOR OVER VOLTAGE ON REAR HO2S (LH) CIRCUIT IN PCM

• Turn the ignition switch to the ON position.

• Rear HO2S (LH) disconnected.

• Measure the voltage for following:

― Between terminal D at the rear HO2S (LH) harness side connector and battery negative post.

― Between terminal B at the rear HO2S (LH) harness side connector and battery negative post.

• Is the voltage greater than 1.5 V?

Yes

Replace the PCM, then go to the next step.

Replace the rear HO2S (LH), then go to the next step.

VERIFY TROUBLESHOOTING OF DTC P0156 COMPLETED

• Make sure to reconnect all disconnected connectors.

• Clear the DTC from the PCM memory using the M-MDS.

• Drive the vehicle at 64 km/h {40 MPH} for at 5 min.

• Is the PENDING CODE same DTC present?

Yes

Replace the PCM, then go to the next step.

(See PCM REMOVAL/INSTALLATION[AJ (3.0L Duratec)].)

Go to the next step.

VERIFY AFTER REPAIR PROCEDURE

• Perform “AFTER REPAIR PROCEDURE”.

(See AFTER REPAIR PROCEDURE[AJ (3.0L Duratec)].)

• Is there any DTC present?

Yes

Go to the applicable DTC inspection.

(See DTC TABLE[AJ (3.0L Duratec)].)

Troubleshooting completed.